Higher Biology - Unit 2.1

​Unit 2.1

Metabolic Pathways ​

​Metabolic Pathways

​Metabolic pathways are a series of chemical reactions that start with a substrate and finish with an end product.

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They are controlled by enzyme-catalysed reactions within cells.

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In plants they can produce​ glucose and cholorophyll, and in animals vitamins and haemoglobin

​The 2 types of metabolic pathways...

​Anabolic

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​Requires energy and is used to build up large molecules from smaller ones (biosynthesis)

​Catabolic

​Releases energy and is used to break down large molecules into smaller ones (degredation)

​Examples of A&C reactions

​Photosynthesis is an example of an Anabolic reaction. In this process plants make glucose molecules from different raw materials

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Food digestion is an example of a Catabolic reaction, as it involves enzymes breaking down food particles so they can be absorbed by the small intestine​

​Proteins and the Membrane

​Enzymes are vital in metabolic pathways, however, some can be found embedded in the cell membranes.

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Proteins found embedded within cell membranes can act as 2 different things...​

​Pumps - For example the sodium potassium cell that pumps sodium out of the cell and potassium into the cell

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Pores - Which allow ions of a particular size to pass through the membrane

Multiple Select

Which of the following substances are created during metabolic pathways in plants?

• Vitamins

• Haemoglobin

• Chlorophyll

• Glucose

Multiple Choice

What is the function of an Anabolic pathway

• To build up large molecules from smaller ones

• To break down large molecules into smaller ones

Multiple Choice

What is the function of a Catabolic pathway?

• To break down large molecules into smaller ones

• To build up large molecules from smaller ones

Multiple Choice

Which of the following processes is an Anabolic reaction?

• Photosynthesis

• Food digestion

Multiple Choice

Membrane-embedded proteins which are controlling the ions entering a cell are behaving as what?

• Pumps

• Pores

​Controlling Metabolic Pathways

​The control of Metabolic pathways is important in order to stop the build up of end products which aren't needed

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This can be done in the presence of a particular enzyme​

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​Controlling Metabolic Pathways

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​If an enzyme is present, the amount of energy needed to make a product is lowered

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As products are made they are no longer in affinity to the enzyme's active site, and are released.

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​Substrate concentration

​The rate of reaction is affected by the concentration of the substrate

​As substrate concentration increases, the rate of reaction also increases...

​Inhibition

​An inhibiter can be used to stop an enzyme from binding to its substrate

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As a result they can directly control the progress of a metabolic pathway

​The three types

​-Competitive inhibition

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-Non-competitive inhibition

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​-Feedback Inhibition

​Competitive Inhibition

​Occurs when an inhibitor binds itself to the active site of the enzyme.

​As a result, this prevents the substrate from binding

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They can compete with the substrate due to their similar molecular shape.

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Increasing the substrate concentration will eventually reverse competitive inhibition, because the substrate will eventually dilute the inhibitor allowing it to bind to the active site, and win the competition.​

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​Non-competitive Inhibition

​Occurs when the inhibitor does not bind to the active site, instead it binds to a different part of the enzyme therefor causing the active site to change shape.

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The substrate is unable to bind to the active sight as a result

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​Feedback Inhibition

​Occurs when the end product attaches itself to the enzyme.

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​This will stop the metabolic pathway and it will not continue until the concentration of the end product decreases.

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This allows further synthesis of the end product to occur

Multiple Choice

If an enzyme is present, which of the following will happen to the amount of energy required to make the end product?

• Increases

• Decreases

Multiple Choice

If the substrate concentration increases, what happens to the rate of reaction?

• Increases

• Decreases

Multiple Choice

What is the function of an inhibiter?

• To increase enzyme activity

• To allow an enzyme to bind to its substrate

• To stop an enzyme from binding to its substrate

Multiple Choice

Which best describes Competitive Inhibition?

• Binds itself to the active site, competing with the substrate

• The product binds itself to the enzyme

• Binds itself to a part of an enzyme and changes the shape of the active site

Multiple Choice

Which of the following best describes Non-competitive Inhibition?

• Binds itself to the active site, competing with the substrate

• The product binds itself to the enzyme

• Binds itself to a part of an enzyme and changes the shape of the active site

Multiple Choice

Which of the following best describes Feedback Inhibition?

• Binds itself to a part of an enzyme and changes the shape of the active

• Binds itself to the active site, competing with the substrate

• The product binds itself to the enzyme

​List of Terms

​Anabolic - Metabolic activity which requires energy and builds up large molecules from smaller ones

Catabolic - Metabolic activity that releases energy and breaks down large molecules from smaller ones

Metabolic Pathway - Enzyme controlled sequence of chemical reactions in cells

Pores - Small gaps in the membrane which allow ions of particular sizes to pass into the cell

​Pumps - Protein in a membrane which carries substances across it by active transport

Competitive Inhibition - The slowing of a reaction rate due to a substance which attaches itself to the enzymes active site instead of the substrate

Non-competitive Inhibition - The slowing of a reaction rate due to a substance which attaches itself to the enzyme, changing the shape of the active sight

Feedback Inhibition - The slowing of a reaction rate due to the end product binding itself to the enzyme​

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​END OF KEY AREA